The present invention relates to an optical gain component having a gain material which is side pumped by laser diodes. The optical gain component can be used in a laser device. In side pumping a laser gain medium, it is desired to achieve both a high average gain value and a uniform gain distribution. The large divergence angles typical of the emission from laser diodes make these goals difficult to achieve.
A prior art side pumping arrangement is described in Welford et al. "Efficient TEM.sub.00 -mode Operation Of A Laser-Diode Side Pumped Nd: YAG Laser", Optics Letters, Vol. 16, No. 23, (Dec. 1, 1991), pp. 850-852. This article describes the side pumping arrangement shown in FIG. 1. FIG. 1 is a cross-sectional view of a prior art gain material 20. This figure shows a cross-section through the optical axis of the gain material 20. The gain material 20 has a semicircular curvature 20a used for collecting and roughly collimating the emission from the pump diodes 22. The pump energy is reflected back through the gain material by a reflective coating on side 20b. The gain material 20 is also cooled along this side 20b. A five-bar stack of laser diodes 22 is located 0.5 mm from the gain material 20 along the side 20a. In this prior art arrangement, the gain is effectively peaked at the location that the diode energy enters the gain material 20.
This geometry has several disadvantages. First, the rod curvature is used for collimating the pump diodes but also restricts the thickness of the laser medium seen by the diode. For this reason, the flexibility of this technique is limited. Second, this geometry allows for laser diode stacks along side 20a only. If additional laser diode stacks are to be used to pump the gain material from different directions, another rod must be included. Finally, since the cooling of the rod is done along the surface 20b, the cooling is one dimensional and non-symmetrical. This results in a thermal wedge as the rod is pumped harder, so that the laser alignment changes with the average pump power. The laser alignment may also change over time as the diode ages. For the same reason, the gain center (centroid of the gain distribution) does not coincide with the thermal lens center.
It is desired to have an improved arrangement for side pumping a gain material in an optical gain component.